It is a well-known fact that in a cellular network, the number of simultaneous communication sessions with terminals in a specific area of a cell being served by a base station, is limited due to a limited supply of communication resources in the network. These restrictions primarily refer to bandwidth allocated for radio communication in the cell but may also pertain to various equipment available in the base station for providing the radio communication. Network operators typically control the radio communication in their cells by allocating a certain amount of bandwidth to individual cells, often referred to as cell planning or frequency planning which may be fixed or more or less dynamically adaptive over time. If the radio traffic in the cell is dense and more sessions are established, it may happen that all bandwidth allocated to the cell becomes occupied with sessions such that no further sessions can be admitted in the cell. Another limiting factor is also the level of radio interference in the cell and its surrounding cells, which should not be allowed to exceed certain limits to ensure proper radio communication in the cell.
It is generally required that emergency calls and other privileged or prioritized sessions must still be admitted, should it become necessary, even in the congested situation described above. In this description, the term “privileged session” will be used to represent any call or other communication session that is deemed to be of higher importance or priority over other non-privileged calls and sessions of no particular importance or priority, referred to as “non-privileged sessions” which thus have no precedence over any other sessions. Some typical examples of such privileged sessions are emergency calls when users in the cell dial a specific emergency number, such as 112 or 911, and communication sessions from or to parties of particular priority such as persons working for public safety and law enforcement, e.g. the police.
When an access request for an emergency call or other privileged session is made in a congested cell, a conventional and obvious solution for the network is to “throw out” an ongoing session of inferior priority in the cell by simply terminating that session and releasing the resources used in the session, to make room for the emergency call. However, this procedure is generally deemed undesirable since the user of the thrown-out session will most likely perceive this action of forcibly ending the call rather annoying and unacceptable. In fact, some countries and regions do not accept or even allow that calls and sessions are thrown out and forcibly terminated in this way.
In this context, it is generally deemed a better solution, at least from the users' viewpoint, to keep resources at the base station reserved in advance exclusively for emergency calls in the cell, to ensure that whenever access for an emergency call is requested there will be enough communication resources free to use for that call with a minimum of delay. Typically, it is not sufficient to pre-reserve resources in this way for just one emergency call but resources must be pre-reserved for a number of such calls, to guarantee the admission of, say, three or four emergency calls at any time, e.g. in the case of an accident. This may even be an official requirement in some countries and regions.
“Pre-reserved” resources means that the resources are set aside and cannot be used for other than privileged sessions. Currently, it is proposed that the network operator decides how much resources to pre-reserve for privileged sessions in each cell, which is done by configuring various resource-related parameters in the respective base stations. A basic requirement is thus to always provide access for privileged sessions in cellular networks.
However, there are some problems and drawbacks associated with the above-described pre-reservation of resources for a number of privileged sessions. Firstly, if each and every cell in a network with numerous cells must keep unoccupied resources reserved for privileged sessions at any time, much capacity in the network will surely go unused since it is very unlikely that a considerable amount of pre-reserved resources will be used for privileged sessions at the same time. Further, an emergency situation typically occurs during a limited time and in a rather limited area, perhaps within a single cell, although which cell that would be cannot be foreseen which is why every cell must have pre-reserved resources just in case. For example, if a network with 10,000 cells and corresponding base stations must pre-reserve resources for three privileged sessions in each cell, resources for a total of 30,000 calls will be practically wasted and go unused. As a result, the wireless networks must be designed with capacity of great excess in relation to the used capacity, which is naturally quite expensive.
Secondly, there may be situations when those pre-reserved resources to guarantee three or four privileged sessions in each cell is still not enough locally, e.g. when a major accident happens and there is need for several emergency calls and calls from/to privileged persons working with the accident and others. Thirdly, considerable efforts are required for configuring each and every cell with surplus resource capacity to make room for a plurality of privileged sessions, should that ever be needed.